Pneumatic vehicle tires essentially consist of a tire carcass, which consists of plies of rubberized fabric, and tread rubber, which surrounds the exterior surface of the carcass. In belted tires, additional layers of fiber glass, steel, or aramid are placed between the plies and the tread rubber. During manufacture, the tire is vulcanized to gain its final shape and strength characteristics. Beside equalizing the stresses within the tire body, the vulcanization changes the rubber compound into a tough, highly elastic material and bonds the parts of the tire into one integral unit.
During the vulcanization process, the tread rubber is molded to form the tire treads which provide frictional engagement between the tire and the road surface. The treads also protect the tire carcass from foreign obstacles on the road surface which could damage the carcass. Since the effectiveness of the tire tread as a cushioning and protective sheath is dependent upon the amount of tread rubber covering the carcass, this effectiveness is decreased as the treads are reduced by wear. If the tire is not routinely inspected, the tread may be worn down to a level where driving becomes dangerous.
In the past, it has been known to form a tire with a layer of a colored material embedded in the tread rubber to visually indicate the degree of tread wear. For example, U.S. Pat. No. 3,261,388 discloses positioning plies having colored fibers at different tread depths to visually indicate when the tread has been worn to the point at which the tread should be recapped or the tire replaced. U.S. Pat. No. 3,516,467 discloses a tire having a sub-surface tread portion of a color contrasting to the outer portion of the tread to indicate when the tread is worn. U.S. Pat. No. 3,516,467 suggests embedding a colored indicating means within the tread portion of a tire. In this case, the indicating means is preferably made from rubber, metal, or plastic. It has also been recognized in the past to incorporate a colored material directly within the tire treads to visually monitor the amount of tread wear, as shown in U.S. Pat. Nos. 2,102,784 and 4,226,274.
Problems have arisen in connection with the abovedescribed colored tread wear indicators in that the coloring in the indicators degrades under the high temperature of vulcanization. Moreover, in instances when the colored material is formed from plastic, the colored material may not sufficiently adhere to the tread rubber. Consequently, after the tire cools following vulcanization, air pockets may remain between the plastic tread wear indicators and the tread rubber, thereby reducing the integrity of the tire.
Another method of visually indicating tread wear involves positioning colored tread markers in the grooves of a tire, as disclosed in U.S. Pat. No. 3,578,055. Shoulder portions are cut or molded into the base of the grooves for receiving the colored markers, which are preferably made from a plastic material.
U.S. Pat. No. 3,653,422 discloses a tire having a traction pattern incorporated in the tread rubber. The pattern only becomes visible when a predetermined amount of the tread rubber remains, thus warning the user that the tire will soon have to be replaced or retreaded. U.S. Pat. Nos. 4,074,742, 3,833,040 and 3,362,376 disclose other tire tread wear indicating systems.
The difficulties suggested in the preceding art are not intended to be exhaustive but rather are among many which tend to reduce the effectiveness of prior tires having colored tread wear indicators. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that such tires for indicating tread wear appearing in the past will admit to worthwhile improvement.
Accordingly, it is therefore a general object of the invention to provide a belted tire which will obviate or minimize difficulties of the type previously described.
It is a specific object of the invention to provide a belted tire which visually indicates the degree of tread wear to warn a user when the tread has been worn to an unsafe limit.
It is another object of the invention to provide a pneumatic or solid belted tire which includes a colored and/or fluorescent and/or solid tread wear indicator structurally designed to maintain its coloring, fluorescence and integrity under the high temperatures of vulcanization.
It is still another object of the invention to provide a tread wear indicator for use with a belted tire which is durable, compact, and economical to manufacture.
It is a further object of the invention to provide a method for forming a tire which visually indicates when the tread has been worn to an unsafe limit.